It would be important to have CreditorDebtorController.php:73 as stated in the error message. Most likely you have an echo, so PHP needs to send an earlier and thus cannot send another one later, or a command there doesn't work, so PHP also sends a(n error) message.

I recognised the server from the error message that was posted. The person who owns this website hires Yii developers, then does not pay them and locks them out of the server.... then brings along the next bunch of devs to dupe.

Thanks for the heads up. I gather he's black listed at the various freelance sites?
If not, he should be.

I'm not sure, however because he has had many devs of various talent work on the website, there are many security flaws. I can bring down the whole website at any time I please, or write to the file system or database, even without access to his cPanel or FTP